CVE-2025-20254 Overview
CVE-2025-20254 is a memory leak vulnerability in the Internet Key Exchange Version 2 (IKEv2) module of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software. An unauthenticated, remote attacker can exploit improper parsing of IKEv2 packets to partially exhaust system memory. Successful exploitation prevents establishment of new IKEv2 VPN sessions and requires a manual device reboot to restore service. The flaw is tracked as [CWE-401] Missing Release of Memory after Effective Lifetime.
Critical Impact
Remote attackers can degrade VPN availability on Cisco ASA and FTD devices without authentication, disrupting new IKEv2 tunnel establishment until administrators reboot the appliance.
Affected Products
- Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
- Cisco Secure Firewall Threat Defense (FTD) Software
- IKEv2 module (component)
Discovery Timeline
- 2025-08-14 - CVE-2025-20254 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-20254
Vulnerability Analysis
The vulnerability resides in how the IKEv2 module parses incoming key exchange packets. When Cisco ASA or FTD Software processes crafted IKEv2 packets, allocated memory is not properly released after use. An attacker generates a continuous stream of these packets toward an affected device, gradually consuming available memory. As memory pressure grows, the system loses the ability to negotiate new IKEv2 VPN sessions and becomes unstable. Recovery requires manual intervention because the leaked memory is not reclaimed at runtime. The issue is classified under [CWE-401] Missing Release of Memory after Effective Lifetime.
Root Cause
The root cause is improper parsing logic in the IKEv2 packet handler. Memory allocated during processing of specific malformed or crafted fields is never freed on the error path, producing a cumulative leak with each processed packet.
Attack Vector
The attack vector is network-based and requires no authentication or user interaction. An attacker sends a sustained flood of crafted IKEv2 packets to any interface where the IKEv2 service is exposed, typically the outside VPN termination interface. Because IKEv2 endpoints commonly face the internet, exposure of vulnerable devices is broad.
No public proof-of-concept code is available. Refer to the Cisco Security Advisory for authoritative technical details.
Detection Methods for CVE-2025-20254
Indicators of Compromise
- Steady, unexplained decrease in free memory reported by show memory on ASA or FTD devices.
- Failures to establish new IKEv2 VPN sessions while existing tunnels remain active.
- High-volume inbound UDP traffic to port 500 or 4500 from a small set of remote sources.
- System instability or crypto subsystem log messages tied to IKEv2 processing.
Detection Strategies
- Baseline IKEv2 packet rates per source and alert on sustained deviations exceeding normal peer negotiation traffic.
- Correlate memory utilization trends with IKEv2 negotiation counters using SNMP or telemetry streaming.
- Monitor VPN session establishment failure rates as a leading indicator of resource exhaustion.
Monitoring Recommendations
- Ingest ASA and FTD syslog into a centralized platform and alert on repeated IKEv2 parse errors.
- Track show memory detail output on a schedule to detect gradual memory consumption trends.
- Enable NetFlow or firewall telemetry on VPN-facing interfaces to identify anomalous UDP 500 or 4500 sources.
How to Mitigate CVE-2025-20254
Immediate Actions Required
- Apply the fixed Cisco ASA and FTD Software releases identified in the Cisco Security Advisory.
- Inventory internet-facing devices running IKEv2 and prioritize patching those terminating remote-access or site-to-site VPNs.
- Establish a maintenance window for a manual reboot if memory has already been partially exhausted.
Patch Information
Cisco has published fixed software versions and remediation guidance in advisory cisco-sa-asa-ftd-ios-dos-DOESHWHy. Administrators should follow the upgrade path listed for their platform and train version. Consult the Cisco Security Advisory for the authoritative fixed-release matrix.
Workarounds
- Restrict IKEv2 peer connectivity using control-plane access lists that permit only known VPN peers to reach UDP 500 and 4500.
- Deploy upstream rate limiting on IKEv2 traffic to slow the accumulation of leaked memory from crafted packet streams.
- If IKEv2 is not required, disable the IKEv2 service on affected interfaces until patching is complete.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
